1. Field of the Invention
The present invention relates to an internal pressure-stabilizing apparatus for stabilizing the internal pressure to establish a space, and an ink tank for. accommodating an ink to be discharged onto the printing paper by an ink-jet printer.
2. Description of the Related Art
Ink-jet printers are known, which perform the printing operation by discharging inks. A known ink-jet printer of this type is provided with an ink-jet head which discharged the ink from nozzles, and an ink cartridge (ink tank) which accommodates the ink to be discharged. Individual ink flow passages, which introduce the ink supplied from the ink cartridge into the respective nozzles, are formed in the ink-jet head. In this arrangement, it is preferable that the internal pressure is maintained within a predetermined range in the ink supply system which ranges from the ink cartridge to the individual ink flow passages in order that the meniscus of the ink is stably retained at a predetermined position in each of the nozzles, and the ink does not leak and drip from the nozzles. For example, the following techniques are known. That is, the internal pressure of the ink supply system is established in accordance with the difference in liquid head by arranging the components such that the position of the ink liquid surface in the ink cartridge is lower than the position of arrangement of the nozzles. The internal pressure of the ink supply system is established in accordance with the capillary force of a porous sponge by arranging the sponge at an ink outflow port of the ink cartridge (see, for example, U.S. Pat. No. 6,502,933 (FIG. 3) corresponding to Japanese Patent Application Laid-open No. 2002-160383).
However, in the case of the former technique, it is impossible to efficiently arrange the ink-jet head and the ink cartridge due to the restriction imposed by the positional relationship between the ink-jet head and the ink cartridge. As a result, the ink-jet printer becomes large-sized. Further, if the entire apparatus is inclined, the positional relationship between the ink-jet head and the ink cartridge is changed. Therefore, it is difficult to apply the former technique to a mobile or portable ink-jet printer. On the other hand, in the case of the latter technique, the viscosity of the ink adhered in the sponge is increased as the time elapses. The flow of the ink is deteriorated. It is difficult to maintain a proper back pressure for the ink supply system. Further, a problem arises such that the sponge is consequently deteriorated due to the use for a long period of time.